The drum type washing machine, washing laundry by using friction between laundry and drum rotated by driving force of a motor in a state detergent, washing water, and the laundry are introduced into the drum, gives almost no damage to the laundry, causes no entangling of the laundry, and provides a washing effect of pounding and rubbing the laundry.
A system in which the driving force is transmitted from the motor to a drum, not directly, but indirectly through a belt wound on a motor pulley, and a drum pulley causes an energy loss and generates much noise in a power transmission process.
In order to solve problems of the related art drum type washing machine, a direct drive drum type washing machine is introduced.
The direct drive drum type washing machine will be described.
There is a stator fixedly secured to a rear wall of a tub which holds washing water therein. A washing shaft has one end connected to a rear wall of a drum in the tub for washing the laundry while rotating, and the other end passed through the rear wall of the tub, and connected to the rotor. The rotor may be an outer rotor which rotates on an outer side of the stator.
As the rotor rotates by an electromagnetic action between the stator and the rotor through above structure, the rotation force is transmitted to the drum directly through the washing shaft.
A structure of the outer rotor will be described with reference to FIGS. 1 and 2.
Referring to FIGS. 1 and 2, the outer rotor ‘R’ is provided with a rotor frame 100 of steel plate, and magnets ‘M’ attached to an inside surface of a side wall 120 of the rotor frame 100, wherein the rotor frame of steel plate has a stepped portion formed in a circumferential direction at a side wall 120 extended from a bottom 110 thereof substantially perpendicular thereto for seating the magnets ‘M’.
Accordingly, since the stepped portion supports the magnets ‘M’ when the magnets ‘M’ are attached to the inside surface of the side wall 120 of the rotor frame 100, fabrication of the rotor is easy.
Moreover, the rotor frame 100 has a plurality of cooling fins 130 around center of the bottom 110 in a radial direction, for blowing air toward a stator (not shown) when the rotor rotates, to cool down heat from the stator.
The cooling fins 130 are formed by lancing in a direction of an opened portion, and pass through holes 140 formed by the lancing serve as vents.
Along with this, there are embossed portions 150 between adjacent cooling fins 130 on the bottom 110 of the rotor frame 100 for reinforcing the rotor 13, each with a drain hole 160 for draining water.
However, the related art outer rotor ‘R’ has the following drawbacks.
At the time of high speed rotation, such as spinning for drying laundry, the drum type washing machine with the outer rotor ‘R’ shows heavy throbbing of the side wall 120 of the rotor frame 100 of steel plate caused by electromagnetic interaction (i.e., attraction and repelling force) with respect to the stator, to generate noise from the motor.
That is, the related art outer rotor is not favorable for a motor output and noise because the opened portion of the related art outer rotor having the magnets mounted thereon is far from the bottom, and, consequently, has difficulty in maintaining balance during rotation of the rotor as much as the distance ‘D’ is great.
Moreover, in a case it is intended to project the cooling fins to an outside of the rotor frame for providing variety in the products, the cooling fins projected as much as lengths of the cooling fins increase a space the motor occupies in the washing machine.
When it is intended to stack the outer rotor before transportation to a production line, or assembly in the production line, the cooling fins of the outer rotor disposed on a lower side are likely to deform due to weight of the rotors stacked thereon.